1. Field of the Invention
The present invention relates to a solid-state imaging device including a charge-transfer portion, such as a CCD solid-state imaging device, a method of manufacturing a solid-state imaging device, and a method of driving a solid-state imaging device.
2. Description of the Related Art
In a CCD solid-state imaging device, a transfer resistor having a CCD structure is provided as a charge-transfer portion, and a signal charge obtained through photoelectric conversion and stored in a light-receiving sensor portion formed of a photodiode is read out to the transfer resistor so that the signal charge is transferred in the transfer resistor.
The transfer resistor includes through an insulation film a transfer electrode formed on a transfer channel in which a signal charge is transferred. In order to transfer a signal charge, it is necessary to apply voltage pulses having different phases from each other to the transfer electrodes adjacent to each other, and also it is necessary to prevent a gap from occurring in the channel. Accordingly, the transfer electrode is made to include two electrode layers of a first and second layers, and the edge of the second-layer transfer electrode is made to somewhat overlap the first-layer transfer electrode (refer to Patent Literature 1, for example).
A schematic constitutional view (plan view) of a CCD solid-state imaging device including a transfer electrode formed of two electrode layers in this manner is shown in FIG. 1.
As shown in FIG. 1, with respect to this CCD solid-state imaging device, light-receiving sensor portions 51 are arranged in the form of a matrix, and a vertical transfer resistor 52 which extends vertically (in the upward and downward directions in the figure) is provided on one side of each column of the light-receiving sensor portions 51 as a charge-transfer portion. Although not shown in the figure, a horizontal transfer resistor is connected to one end of the vertical transfer resistor 52.
Further, with respect to the CCD solid-state imaging device shown in FIG. 1, a sectional view of the vertical transfer resistor 52 is shown in FIG. 2A, and a sectional view of a portion between light-receiving sensor portions 51 adjacent to each other in the vertical direction, namely a portion between pixels, is shown in FIG. 2B. Note that in FIGS. 2A and 2B, description of semiconductor regions (each region in a light-receiving sensor portion, a transfer channel region and the like) in a semiconductor substrate is omitted.
The vertical transfer resistor 52 includes a transfer electrode 53 and a transfer channel region (not shown in the figures) formed in a semiconductor substrate 54, constituting a charge-transfer portion of a CCD structure.
Further, as the transfer electrode 53, transfer electrodes 53B and 53D formed of a first electrode layer and transfer electrodes 53A and 53C formed of a second electrode layer are alternately disposed in the vertical direction.
In addition, the edges of the transfer electrodes 53A and 53C of the second layer somewhat overlap the transfer electrodes 53B and 53D of the first layer in the vertical transfer resistor 52.
Recently, to cope with the increase in pixel numbers and miniaturization of a digital camera, a pixel cell of a solid-state imaging device has been improved to be minute.
Hence, in order to obtain high sensitivity as well as miniaturization of a pixel cell of a solid-state imaging device, higher light-receiving efficiency is desired.
However, in the CCD solid-state imaging device including the transfer electrode 53 in which two electrode layers overlap, as shown in FIG. 1 and FIGS. 2A and 2B, projections and cavities around the light-receiving sensor portion 51 become large at the overlapped portions of the transfer electrode 53, so that incident light is partially blocked by the portion.
Hence, it is difficult to improve the efficiency in receiving light.
The overlapped portion of the transfer electrode 53 has normally the thickness of 1 μm or more, so that particularly when the size of a pixel cell is 3 μm or less and the width of an opening on the light-receiving sensor portions 51 is reduced to 1 μm or so, incident light may be partially blocked by the overlapped portions.
[Patent Literature 1] Published Japanese Patent Application No. H9-312390